The invention relates to the field of manufacturing methods for magnetic transducers (heads) and more particularly to methods and structures for monitoring the results of a manufacturing process for producing fine structures used as pole tips in magnetic transducers.
A typical prior art magnetic head and disk system is illustrated in FIG. 1. In operation the head 10 is supported by a suspension 13 as it flies above the disk 16. The magnetic transducer, usually called a xe2x80x9chead,xe2x80x9d is composed of elements that perform the task of writing magnetic transitions (the write head 23) and reading the magnetic transitions (the read head 12). The electrical signals to and from the read and write heads 12, 23 travel along conductive paths (leads) 14 which are attached to or embedded in the suspension arm (not shown). Typically there are two electrical leads each for the read and write heads. Wires or leads are connected to these pads and routed in the suspension 13 to the arm electronics (not shown). The disk 16 is attached to spindle 18 that is driven by a spindle motor 24 to rotate the disk. The disk 16 comprises a substrate 26 on which a plurality of thin films 21 are deposited. The thin films include ferromagnetic material that is used to record the magnetic transitions in which information is encoded.
The write head 23 portion of the transducer typically includes two pole pieces (P1 and P2 formed from ferromagnetic material) (not shown) and a coil (not shown). To decrease the side writing and, therefore, to reduce the track width the pole pieces are shaped into narrow tips at the gap. In a typical prior art method P1 is deposited first and initially has a broad, flat tip that is subsequently ion milled (sometimes called xe2x80x9cnotchingxe2x80x9d) using the P2 tip as a mask to form the P1 tip. This process insures that P1 and P2 have a closely matched tip size. U.S. Pat. No. 6,111,724 to Hugo Santini discusses a prior art process for making P2 tips and describes an improvement using a zero-throat-height defining layer.
Regardless of the method used to form P2, the width of the track written by this type of inductive head is largely determined by the width of the bottom of P2 (P2b). P2 tends to be wider at the top (away from the gap) which creates an additional complication in measuring the width of P2b. It is important to be able to measure P2b with some precision to monitor the manufacturing process. There are numerous variables in the process which affect the formation and shape of P2 including those affecting the photolithography used to define the shapes, the plating process used for depositing the ferromagnetic material, the seed layer removal process and the ion milling used to shape P1 using P2 as a mask. These variables can change from time to time in the manufacturing process and may even vary across a single wafer.
Thus, there is a need for an efficient method of measuring the width of P2b from wafer to wafer and also across each wafer.
Applicant discloses a method for forming metrology structures on a wafer, on which magnetic transducers are being fabricated, which have a measurable electrical resistance which is an accurate surrogate for a physical dimension of the nearby P2 tip structures formed on the wafer for the magnetic transducers. The metrological structure of the invention is formed in parallel with and proximate to the production P2 structure to subject the metrology structure to the same local process variables affecting the P2 production structure, including those which result in the bottom being narrower than the top. The metrology structure is preferably a resistor with pads which are usable with a four point probe. The resistor is preferably formed by creating a sacrificial P2 structure over a pad of millable resistive material. A selected area of the P2 structure is used as a milling mask to replicate the width of the selected area in the resistive material. The selected area should include the narrowest area of P2. Preferably an ion milling process is used to remove the resistive material outside of the masked area of the resistor pad, thus replicating the width of P2 in the resistive material. Since the resistor pad is under P2, it is milled down to the width of the bottom of P2, i.e., P2b. Control structures with unmilled pads of resistive material (sheet resistors) are formed along with the metrology structures to provide the sheet resistance of the pads prior to milling. Knowledge of the sheet resistance allows the resistance of the milled structure to be converted into an accurate measure of the physical dimension.
The metrological structure of the invention provides a way to measure the width in a more convenient way than is available in the prior art. In addition, since ion milling of the P1 tip using the P2 tip as a mask is already a typical part of the prior art process of manufacturing transducers, the metrology structure can be milled at the same time and in the same way.